Intramolecular nickel catalyzed cycloadditions of bis-dienes: 3 approaches to the taxane skeleton

The successful application of the nickel catalyzed, intramolecular [4+4] cycloaddition of bis-dienes to the preparation of both the AB and BC ring systems of the taxane diterpenes is described. This cycloaddition methodology provides the basis for a general and efficient route to angularly alkyl-substituted bicyclo[6.4.0]dodecanes and to bicyclo[5.3.1]undecanes.     

Material Basis Elucidation and Quantification of Dandelion through Spectrum–Effect Relationship Study between UHPLC Fingerprint and Antioxidant Activity via Multivariate Statistical Analysis

The excessive expression of reactive oxygen species is closely connected to many diseases. Considerable studies have demonstrated dandelion as well as its ingredients exhibited antioxidant activity. However, specific material basis reflecting the antioxidant activity has not been comprehensively investigated. In this study, a spectrum–effect relationship study on dandelion between fingerprinting and antioxidant activity was analyzed in detail, while a UHPLC quantification method developed and completely validated for simultaneous determination of active ingredients in dandelion. With the establishment of dandelion fingerprints of different regions, 24 common peaks were characterized. The classic FRAP method and ABTS methods were then used to detect their antioxidant activity. Partial least squares regression analysis, bivariate correlation analysis and grey correlation method were used to accomplish the spectrum–effect relationship. Eventually, the ingredients with antioxidant activity which could be considered as candidate quality markers of dandelion were discovered through spectrum–effect relationship analysis. The six compounds including caftaric acid, chlorogenic acid, caffeic acid, chicoric acid, isochlorogenic acid A, and isochlorogenic acid C were quantitatively determined. The developed UHPLC assay method was accurate, precise, and reliable. The study has elucidated the antioxidant material basis of dandelion and provided a scientific basis for the quality control of dandelion.     

Theoretical Calculations for Structural, Elastic and Thermodynamic Properties of MgB2 under High Pressure

We have investigated the structural and elastic properties of MgB₂ under high pressures using the full-potential linearized muffin-tin orbital (FP-LMTO) scheme within the generalized gradient approximation correction (GGA) in the frame of density functional theory. The calculated pressure dependence of the normalized volume is in excellent agreement with the experimental results. At the same time the elastic constants and acoustic anisotropy as a function of applied pressure are presented. Through the quasi-harmonic Debye model, we also investigate the thermodynamic properties of MgB₂.     

含有络合功能基的非天然氨基酸的设计、合成及在生物活性肽中的应用

设计合成了一类侧链带有络合基团的非天然氨基酸, 即侧链带有N,N-二羧甲基氨甲基、N,N-二酰胺甲基氨甲基和N,N-二羟乙基氨甲基的苯丙氨酸衍生物, 并将这类非天然氨基酸用于促性腺激素释放激素(LHRH)类似物的固相合成. 高效液相色谱分析结果表明, 粗肽的纯度较好, 易于纯化; 用电喷雾质谱测定了多肽的分子量. 这些非天然氨基酸可作为其它肽类药物合成的构建单元.     

A high yield synthesis of biferrocenyl

Biferrocenyl has been obtained in 78% yield by reaction of monolithioferrocene with p-xylene dibromide.     

ZnO:V3+晶体光谱和电子顺磁共振谱的理论研究

采用强场耦合图像,建立了3d2电子组态在三角对称中的45×45能量矩阵,通过对角化完全能量矩阵的方法,计算出了ZnO:V3 晶体的45条光谱能级和5个电子顺磁共振谱参量(零场分裂D,g因子g//,g⊥和超精细结构常数A//,A⊥),计算结果与实验数值能很好地符合.计算中还发现V3 杂质中心的局部结构与基质晶体的结构不一致,即V3 在ZnO中并不占据准确的Zn2 位置,而是沿c3轴方向位移一段距离△Z≈0.003 nm.作者对上述这些结果的合理性进行了讨论.     

Structure and composition of the Pt(s) [6(111) × (111)] step-terrace surface vs. pH and potential in aqueous Br− solutions: Studies by LEED and Auger spectroscopy

Experiments were performed in which a well-characterized Pt(s) [6(111)×(111)] surface (consisting of terraces five atoms wide separated by steps of one atom height) was immersed into aqueous CaBr₂ solutions at controlled potential, after which the surface was removed from solution, evacuated and characterized by LEED and Auger spectroscopy. Adsorption of Br was strongest from acidic solutions, displaying a maximum of θ_Br = 0.5 (Br per surface Pt atom) near 0.2 V (vs. Ag/AgCl reference). At packing densities near the maximum, the Br layer displayed Pt(s) [6(111)×(111)](3×T) LEED patterns, which were relatively diffuse, indicating imperfect long-range order with a repeat distance of three PtPt distances parallel to the steps. Chemisorbed oxides or hydroxides were formed at relatively positive potentials. A streaked Pt(s) [6(111)×(111)] (9×NT) LEED pattern was found at potentials where oxidation led to similar Br and O/OH packing densities, indicating the presence of a seven-unit repeat distance parallel to the Pt steps and a variable multiple of the terrace width perpendicular to the steps. Retention of Ca²⁺ ions by the surface was potential dependent, with a minimum which coincided with the Br maximum, θ_Ca = 0.02. Water was retained by the surface due to interaction with Ca²⁺ to the extent of 5–15 water molecules per Ca²⁺ ion, depending upon the pH and potential. Comparison of these data with similar results for atomically smooth Pt (111) surfaces revealed that bromide was not selectively adsorbed at steps of the Pt surface.     

Modelling of repulsive potentials from atom charge density distributions: interactions of inert gas atoms

Using electron charge density overlap integrals, a correlation procedure for estimating short-range repulsive intermolecular potentials has been investigated. It is found that the repulsive potentials correlate well with the density overlap integral divided by the square of the distance. A simple combining rule for inert gas atoms is obtained and compared with an accurate determination of repulsive potentials for all the mixed rare gases and with other combining rules.     

Facile synthesis of fluorine containing imidazo [1,2-b] [1,2,4] triazines through α-oxo-n-aryl-α arylethanehydrazonoyl bromides

Treatment of fluorine containing arylglyoxals with aminoguanidine bicarbonate in aqueous ethanol formed fluorinated 3-amino-5-aryltriazines which in turn ontreatment with α-oxo-N-aryl-α-arylethanehydrazonoyl bromides afforded 3,6-diaryl-7-arylazoimidazo[1,2-b][1,2,4] triazines in 75–80% yield. All the compounds were characterized by their analytical and spectral (IR, PMR and Mass) data. Mass fragmentation patterns of these compounds have also been discussed. The screening of biological activities are in progress.